The overall goal of this project is to examine immunological mechanisms which may involved in the pathogenesis of autoimmune diseases such as multiple sclerosis (MS) and chronic Lyme disease of the nervous system. Specifically, the antigen recognition of T lymphocytes from patients with disease such as MS and chronic Lyme disease are examined with respect to the specific antigens (foreign and autoantigens) recognized and their functional phenotype, i.e., whether they secrete pro- inflammatory cytokines. Furthermore, based on our studies, we are designing novel immunotherapies for MS and started testing one of these, i.e. the use of altered peptide ligands (APL)in MS patients in a phase II clinical trial. The latter trial is currently ongoing at NIB, NINDS, NIH. Seven patients have been enrolled, and we are studying clinical parameters, measure disease activity by magnetic resonance imaging, and perform multiple immunological studies in order to assess the mechanism of action of APL and deepen our understanding of the immune pathogenesis of MS. Another important project currently being pursued in our laboratory addresses the question which foreign antigens, e.g., viruses or bacteria, may trigger the initiation or exacerbations of disease via a mechanism referred to as molecular mimicry. This concept refers to cross-recognition between autoantigens, e.g., derived from the myelin sheath, and antigens derived from foreign agents. For this purpose, we currently employ a novel methodology called combinatorial peptide libraries in the positional scanning format (ps-SCL) together with bioinformatic approaches to identify the entire spectrum of stimulatory ligands for autoreactive T cell clones derived from MS patients. In brief, we test T cell clones with ps-SCL, which represent highly complex mixtures of trillions of peptides, and deduce stimulatory peptide sequences from these assays before we screen the data bases of all known protein sequences for potential stimulatory peptides. This technique has allowed us to identify a number of Borrelia burgdorferi peptides, the causative agent of Lyme disease, and from autoantigens, for a clone that had been isolated from the cerebrospinal fluid of a patient suffering from chronic CNS Lyme disease. Thus, we could show for the first time that one can identify the target specificity for an organ-infiltrating T cell clone that had been expanded by a crude lysate of the whole bacterium. We are currently in the process of developing this methodology further and anticipate that the combination of ps-SCL and biometric data analysis will lead to advances in the identification of target antigens for autoimmune diseases, but also for tumor-specific lymphocytes or T cells that are involved in infectious disease. As an example for the latter, our data for organ-infiltrating T cell in chronic nervous system Lyme disease already suggests that the immune response in the chronic stage of the disease is directed against tissue autoantigens and that this process is thus very similar to an autoimmune disease. - Multiple Sclerosis, Autoimmunity, T cell,